This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is a new collaboration aimed at a developing a new model system that can be used to address problems relevant to cardiac muscle. The tobacco hornworm moth (Manduca sexta) has been a common laboratory organism to study many aspects of physiology. Although there is a fairly extensive literature on the physiology of Manduca flight muscle very little is known about its ultrastucture. The best studied insect flight muscle system is the asynchronous indirect flight muscle of Lethocrus. Unlike Lethocerus, the flight muscle of Manduca is synchronous, i.e. more like skeletal and cardiac muscle of humans. Furthermore, the force/length behavior of Manduca flight muscle is very cardiac-like and it appears to have something like the Frank-Starling mechanism for correcting for instantaneous power requirements. The goal of this preliminary study was to determine what kind of structural information from x-ray diffraction patterns could be gathered from this muscle that could be related to its physiology